Myocarditis is an autoimmune inflammatory heart disease which may lead to dilated cardiomyopathy (DCM), fibrosis and heart failure. Cardiac myosin is the dominant autoantigen in inflammatory heart disease, and it can induce myocarditis in susceptible animal models. In humans, elevated antibody responses against cardiac myosin and its peptides in the S2 hinge region are associated with myocarditis, but T cell responses to cardiac myosin epitopes in human myocarditis/DCM are not defined. Furthermore, the immunopathogenesis of autoimmune myocarditis/DCM in humans is unpredictable with few known biomarkers in humans, and the underlying mechanisms in the subtypes of human myocarditis have not been identified in humans. In our continuation, we will investigate links between innate and adaptive immunity against cardiac myosin. We plan to evaluate a group of myocarditis/DCM patients to determine the immunological parameters of myocarditis progression, DCM, and heart failure and to address the following specific aims which will be a significant step forward in defining the immune phenotypes which control the outcomes in human myocarditis. In Aim 1, we plan to phenotype Th1, Th2, Th17, and Treg cell subsets in human myocarditis/DCM and correlate the blood phenotype with heart biopsy phenotype. We will correlate Th1, Th2, Th17, and Treg T lymphocyte subsets with myocarditis subtype and fibrosis in heart biopsies (lymphocytic, eosinophilic, and giant cell myocarditis subtypes). We wil ascertain sex differences in biomarkers that correlate with myocarditis subtype and disease progression to fibrosis and heart failure. In Aim 2, we will define human T cell epitopes (Th1, Th2, Th17, and Treg) to human cardiac myosin peptides particularly in the S2 hinge region of human cardiac myosin in human myocarditis/DCM, and we will determine individual T cell responses against human cardiac myosin and peptide groups from the S2 hinge region and light meromyosin (LMM) rod regions in human myocarditis/DCM. We will map human cardiac myosin T cell epitopes by ELISPOT (Th1, Th2, and Th17) in human myocarditis/DCM and HLA type individuals in our cohort to determine if there is a correlation or match between HLA haplotype and epitope specificity. In Aim 3, we will phenotype the monocyte/macrophage subsets in human myocarditis/DCM. We will determine the ability of human cardiac myosin TLR ligands to polarize human monocytes/macrophages to become M1 pro-inflammatory or M2 pro-fibrotic phenotypes. We will determine M1/M2 monocyte/macrophage phenotype in the blood of human myocarditis/DCM and compare the ratio of M1/M2 to the macrophage phenotype/fibrosis in heart biopsy, and we will identify the pro- inflammatory/pro-fibrotic transcriptome of sorted CD14+ monocytes and correlate ratio of protective vs profibrotic transcriptome phenotype with outcomes in human myocarditis/DCM.